This invention relates to liners or inflations for teat cup assemblies of vacuum-operated milking machines and, more particularly, to such liners or inflations including a milking tube section which extends from a teat cup shell and is attached to the nipple of the milking machine claw.
Automatic milking machines employ teat cup assemblies including a hollow, rigid outer shell which is attached to a pulsating vacuum line and a resilient, tubular liner or inflation installed in the shell in a manner to form a seal at both ends of the shell. The cow's teat is inserted into the upper end of the inflation and the lower end is connected to a so-called claw of milking machine. During the milking operation, the teat cup assembly is suspended from a cow's teat, primarily by the engagement between an opening or mouth in the upper or head end of the inflation and the cow's teat and milk flows through the inflation under the influence of a vacuum maintained in the milking machine claw.
One type inflation is a one-piece unit including an upper or shell section adapted to fit inside the shell and a lower or milking tube section which is pulled through and extends from an opening in the lower end of the shell and is adapted to be connected to the nipple of the milking claw.
Another type inflation includes an upper or shell section having a lower end which fits through an opening in the lower end of the shell and a separate milking tube section which is connected to the lower end of the shell section via a rigid, sleeve connector which is press-fitted inside the lower end of the shell section.
A further type inflation includes an upper shell section having a lower end which is adapted to be folded back over the open lower end of the shell and a separate milking tube section having a cup-shaped upper end adapted to fit over the folded back portion of the shell section.
The following United States patents are representative of prior art constructions for milking tube sections of milking inflations:
______________________________________ Patentee Patent No. Issue Date ______________________________________ Green 2,099,884 November 23, 1937 Scott 2,341,953 February 15, 1944 Hein 2,694,379 November 16, 1954 Norton 3,611,993 October 12, 1971 Olander 4,196,696 April 8, 1980 Larson 4,324,201 April 13, 1982 Larson 4,372,250 February 8, 1983 ______________________________________
Originally, the inside diameter of the flow passage through the milking tube section of milking inflations could be relatively small because milk flow was quite small. The milking tube section was quite flexible because the small inside diameter permitted the walls to be made relatively thin and still not collapse when subjected to a vacuum during the milking operation. This flexibility permitted the teat cup to be conveniently lifted up and slipped onto a cow's teat without imparting a significant side force on the teat.
Modern dairy cows produce milk at substantially higher flows and, consequently, it has become necessary to increase the inside diameter of the milking tube section in order to accommodate this increase in milk flow. As the inside diameter of the milking tube increases, the wall thickness also must be increased to prevent the walls from collapsing during the milking operation. The increased wall thickness makes the milking tube section relatively stiff.
This stiffness resists movement of the shell into proper orientation for attachment to a cow's teat and can cause the mouthpiece of the inflation to engage a cow's teat at an angle and/or to exert a side force on the teat. This can cause discomfort for the cow. More importantly, such a side force can cause the opening to become slightly distorted, resulting in a non-uniform seal around the teat and undesirable admission of air through the mouthpiece opening which can cause slurping and produce unhealthy conditions for the teat.
The above-identified Hein U.S. Pat. No. 2,694,379 discloses forming a weakened portion of reduced wall thickness in the milking tube adjacent the milker claw. This weakened portion is designed to cause the milking tube to collapse or crimp and shutoff air flow therethrough when a teat cup falls off a cow's teat. Thus, such an arrangement could not be used to solve the above-described problem.